At the present time, all states in the United States have a building code requirement that on certain commercial buildings, the exterior walls and roof must be constructed with noncombustible materials. When exposed to fire (1,700 degrees Fahrenheit (.degree.F.)), materials used are to be noncombustible and not give off toxic fumes. In order to meet the requirement, the exterior of these buildings have been constructed with some or all of the following materials: concrete, brick, block, steel, and fire rated drywall. Blocks and/or steel studs make up the main body of these exterior walls, with brick veneer, stucco, or other finishing material applied to the exterior surface. Although the above named materials are noncombustible, nonmelting, and do not give off toxic fumes when exposed to fire, they are extremely poor insulators against the heat and cold. For instance, hollow concrete blocks (light aggregate) have the resistance (R) values as follows: 4-inch (4") block--R-1.11; 8-inch (8") block--R-1.72, and 12-inch (12") block--R-1.89. Even though the steel stud wall can be filled with thermal insulation, the steel stud itself will be a thermal conductor between the exterior and the interior of the building. Consequently, for these buildings to be habitable, these walls will require an additional thermal insulated wall or ceiling to protect the interior of the building from the heat of summer and the cold of the winter. When the concrete, brick, block, steel and fire rated drywall materials are used in exterior walls and roof area, they presently must all be built on site with expensive materials and field labor, thus maintaining high cost and adding time to the construction financing.
Further, the use of concrete blocks requires appropriate concrete footings and supports for the wall and foundation and attention to the weight of the materials, for example, the weight of hollow concrete blocks (light aggregate) must be considered in providing footings. A 4" block weighs 21 pounds per square foot, an 8" block weighs 38 pounds per square foot, and a 12" block weighs 55 pounds per square foot. This significant difference in square footage weight means the modular building panel requires less weight to be borne by the concrete footings and wall (foundation). The extra supports and footings add to the cost of the block walls.
Thus, a problem in the art is the construction of affordable buildings that meet code requirements. In addition to block and/or steel stud construction, the person of ordinary skill in the construction industry has attempted to solve the problem of providing affordable buildings in other ways. Some commercial buildings have been produced with a single metal skin. These buildings meet fire codes but have very high heating and cooling costs because there is little or no insulation. Other commercial buildings utilize steel framing, to which is applied 4" or 6" fiberglass insulation along with a metalized vinyl facing sheet, to the framing walls and roof. An exterior steel rib panel is applied using self drilling/self tapping stitching screws which drill a hole through the steel rib panel, through the insulation and fasten into the framing. Because of this procedure, every stitching screw that is fastened into the framing becomes a thermal conductor of cold and heat to the framing. In cold weather and with the interior heated, these cold areas on the framing will cause moisture and frost to form, damaging the insulation. Over a period of years, the moisture will cause the exterior steel rib panel to rust from the inside out.
Yet another insulation system is known to commercial contractors. This system allows the contractor to install 8" to 12" of insulation into the roof assembly. This insulation includes an interior metal skin, 8" to 12" insulation blocks, and the exterior metal rib skin. The system does eliminate the moisture and frost problem, but the drawback is that it must be applied to the roof area one piece at a time, adding construction costs to the roof area.
When a state building code designates building projects be built with exteriors of noncombustible materials, traditional building methods use masonry, hollow concrete blocks and/or steel studs as their main wall assembly and a steel roof system in these projects. Each of the conventionally produced wall systems requires a thermal insulated barrier wall between the main exterior walls and the interior of the building. This process adds cost and time to construction financing and the completion date. It will take two extra steps in scheduling and personnel to finish the exterior walls and attic ceiling: first a framing crew, to site build the barrier walls and ceiling; and second, an insulating crew to install the needed insulation.
Another approach to modular buildings employs sandwich panels. Prefabricated modular building panels, sandwich panels, generally are formed of a pair of spaced apart walls, surfaces, or skin sheets, having inserted therebetween some kind of insulating core material. In these conventional sandwich panels, the skin sheets bear all the loads and the core has an insulating function as well as the additional function of holding the facing skin sheets in spaced relationship under load. The core bears both tension and compression loads which are normal to the surfaces of the facing sheets. The structural loads imposed on the panels are borne almost totally by the skins. In recent years, a variety of foamed polymers (e.g., polyurethane and polystyrene) have been used as the insulating core material for such modular building panels. Various problems, however, have been encountered in the design and structure of modular building panels.
The majority of sandwich panels are produced by injecting an insulating foam product between the exterior and interior skins, or by gluing the exterior and interior skins to blocks of foam. This foam provides the necessary insulating properties. However, when the sandwich panels are exposed to fire, the foam melts, gives off toxic fumes and causes the exterior and interior skins to separate, thereby losing mechanical strength.
Another group of sandwich panels utilize subgirts in their construction. For sandwich panels using mineral wool as the insulation, the subgirts have been found to be made from fire rated drywall, fiberglass, plastic and steel. Sandwich panels using fire rated drywall as their subgirt do not have the mechanical integrity (strength) to support an exterior wall covering; consequently, their use is limited to interior fire rated walls. Sandwich panels that used fiberglass or plastic as their subgirt are noncombustible and do not give off toxic fumes when exposed to fire, but the subgirt melts causing the exterior and interior skin to separate. These panels must have fire rated drywall applied to the interior skin to maintain any integrity. Sandwich panels that use steel as their subgirt have the same problem as the steel stud wall. The steel subgirt becomes a thermal conductor of cold and heat, and needs an interior thermal insulated barrier wall next to the exterior wall. Thus, the industry has struggled to find ways to integrate, into a modular building panel, the combination of thermal insulation, mechanical strength for load bearing purposes desired for the panel, fire resistance and/or other desired properties.
There have been various prior art attempts to provide improved panels. For example, U.S. Pat. No. 4,641,469 issued to Wood teaches a modular panel made with polyurethane foam board or polystyrene foam board. Flanged rigidifying channels are inserted into the foam board by sliding them lengthwise into channels cut into, and extending across, the foam board. At the construction site, the board is attached to the building structural members by use of the rigidifying channels.
In U.S. Pat. No. 4,961,298 issued to Nogradi, "C-shaped" aluminum rigidifying channels are embedded into the foam board by transverse movement of the channels relative to the foam board, and are held to the board by adhesive. At the construction site, the board is glued to a substrate wall surface.
Both Wood and Norgadi teach using light-weight coatings on the board surface. Typical coatings are acrylic-based coatings or cementitious materials. Neither Wood nor Nogradi teach any reinforcing means extending between the two outer surfaces of the modular building panel. Accordingly, they are unable to provide any structural connection between the building structural members and the surfaces of the modular building panels which are disposed outwardly of the building. The panels of Wood and Nogradi lack the ability to secure heavy components, such as brick, on the outside surface of such modular panels to the structural members of the building, by connection through the elements of the modular panel. Accordingly, both the Wood and Nogradi panels lack mechanical strength. Neither do they offer a noncombustible insulating panel or protection from penetration of ballistic projectiles.
U.S. Pat. No. 4,837,999 issued to Stayner teaches a modular insulating panel made with a foam board core member, and having fiberglass-impregnated and/or filler-impregnated "C-shaped" or "H-shaped" thermoset resin pultrusions on opposing edges of the foam boards and extending between the inner and outer surfaces of the modular panel. The pultrusions in Stayner can perhaps provide a reinforcing connection between the building structural members and the outer surface of the building modular panels, while maintaining a reasonable thermal barrier between inner and outer surfaces of the modular panels at the pultrusions. But the polymer resin-based pultrusions inherently comprise a continuous-phase embedding polymeric material which receives the reinforcing fiberglass and/or any filler used. Accordingly, while the pultrusion may have a lower fire spread rate, it can contribute fuel to the burning of a fire. Of even greater concern, the polymer-based pultrusion can melt. Stayner makes no claim that his pultrusion is noncombustible or nonmelting. Rather, he suggests using noncombustible mineral wool for some or all of the core member of the modular panel, in order to reduce or eliminate combustibility of the core member. His only suggestion that offers elimination of the combustibility of the pultrusions is to replace the pultrusions with corresponding members made with metal. Stayner admits that such metal members would compromise the insulating value of the modular panels. He does not address the susceptibility of his polymer to melt. Stayner offers no mechanical reinforcing means and no bullet-proofing.
Thus, a persistent and vexatious problem in the art is the lack of a modular panel having the combination of good thermal insulation and mechanical load bearing properties, as well as maintenance of structural integrity during fire conditions; namely noncombustible and nonmelting properties, preferably including reinforcing connections between the building structural frame and the outer surface of the outer wall of the building. Neither does the art teach or suggest a light weight modular building panel offering substantial protection from penetration of ballistic projectiles. Despite recognition of these design problems, proper solutions to these problems have not been demonstrated in the art.